Currents activated maximally by extracellular alkalization and halothane are not occlusive in motoneurons or in rTASK-1-expressing HEK 293 cells. A,Membrane current in a hypoglossal motoneuron held at −60 mV was shifted outward by an alkalized solution, pH 8.4, and by halothane (1.25 mm). In the continued presence of halothane, the current induced by pH 8.4 solution was still evident (and indeed enhanced). B, Averaged data (± SEM,n = 10) depicting the I–Vrelationship of the current induced by alkalized solution in the presence of halothane. The data were derived by subtraction of currents induced by halothane from those obtained in the pH 8.4 solution in the continued presence of halothane (inset). This additional current evoked by extracellular alkalization was well fitted by using the GHK constant field equation. C, The conductance in HEK 293 cells expressing rTASK-1, determined by using ramp voltage commands, was increased by halothane (1.25 mm) when the pH-sensitive current was enabled by an alkalized extracellular solution (pH 8.4), but not after blocking the pH-sensitive conductance with an acidic solution (pH 6.5). Inset, Averaged data (± SEM,n = 6), depicting the halothane-induced conductance (G halothane) as a percentage of the total pH-sensitive conductance (G pH = G_8.4 − G_6.5), show the complete block of halothane effect in acidified extracellular solution.D, The I–V relationship of the halothane-sensitive current in alkalized solution was derived from ramp voltage commands and was well fitted by using the GHK constant field equation.